Generally speaking, a display device of a non-self-emitting type, e.g., a liquid crystal display device, causes changes in the transmittance (or reflectance) of a display panel with a driving signal so as to modulate the intensity of light from a light source which is radiated on the display panel, thus displaying images or text. Such display devices include: direct-viewing-type display devices, which allow images or the like displayed on a display panel to be viewed directly; and projection-type display devices (projectors), which allow images or the like displayed on a display panel to be projected in an enlarged form on a screen by means of a projection lens. As non-self-emitting type display panels other than liquid crystal display panels, electrochromic display panels, electrophoresis-type display panels, toner display panels, PLZT panel, and the like are known. Currently, liquid crystal display devices are widely used in monitor devices, projectors, mobile information terminals, mobile phones, and the like.
In a liquid crystal display device, by applying a driving voltage corresponding to an image signal to each of the pixels which are regularly arranged in a matrix, the optical characteristics of the liquid crystal layer in each pixel are changed, whereby image, text, and the like are displayed. As a system for applying independent driving voltages to the aforementioned pixels, there are a passive matrix system and an active matrix system. A liquid crystal display panel of an active matrix system needs to be equipped with switching elements and lines for supplying driving voltages to pixel electrodes. As switching elements, non-linear two-terminal devices such as MIM (metal-insulator-metal) devices and three-terminal devices such as TFT (thin film transistor) devices are used.
When intense light impinges on the switching elements (especially TFTs) which are provided on the display panel, the devices' resistances in their OFF state are decreased. This results in a problem in that the charge which each picture element capacitor acquired during voltage application is discharged, thus making it impossible to obtain a predetermined displaying state, so that light will leak even in a black state and the contrast ratio will decrease.
Therefore, in a liquid crystal display panel, with the purpose of preventing light from impinging on TFTs (especially channel regions), a light shielding layer (called a black matrix) is provided on a TFT substrate having TFTs and pixel electrodes formed thereon, as well as on a counter substrate which opposes the TFT substrate via a liquid crystal layer, for example. In a reflection type liquid crystal display device, the effective pixel area will not decrease if reflecting electrodes are utilized as a light shielding layer. However, in a liquid crystal display device which performs display by utilizing transmitted light, the effective pixel area will be reduced by the provision of a light shielding layer in addition to the non-light-transmitting TFTs, gate bus lines, and source bus lines. As a result, the ratio of the effective pixel area to the total area of the displaying region, i.e., the aperture ratio, will be decreased.
Furthermore, this tendency becomes more prominent as the liquid crystal display panel increases in resolution and becomes smaller in size. This is because, even if the pixel pitch is decreased, the TFTs, bus lines, and the like cannot be made smaller beyond certain sizes, due to constraints in terms of electrical performance, production technique, and the like.
In particular, in a transflective type liquid crystal display device, which have gained prevalence as display devices for mobile devices such as mobile phones in the recent years, each pixel has a region (a reflecting region) which performs display in a reflection mode and a region (transmitting region) which performs display in a transmission mode. Therefore, by reducing the pixel pitch, the ratio of the area of the transmitting regions to the total area of the displaying region (i.e., the aperture ratio of the transmitting regions) will be greatly decreased.
Under dim lighting, a transflective liquid crystal display device performs display by utilizing light from a backlight which is transmitted through the liquid crystal display panel, and under bright lighting, performs display by reflecting light from the surroundings. Thus, a transflective liquid crystal display device is able to achieve display with a high contrast ratio regardless of the surrounding brightness, but has a problem in that its brightness decreases as the aperture ratio of the transmitting regions is decreased.
In particular, the efficiency of light utility (i.e., brightness) will decrease even more in a direct-viewing-type liquid crystal display device or a single-panel projector which performs color displaying by utilizing absorption of light by color filters.
As one method of improving the efficiency of light utility in projection-type liquid crystal display devices, a method has come into practical use in which microlenses for converging light on the respective pixels are provided on the liquid crystal display panel to improve the effective aperture ratio of the liquid crystal display panel. Most conventional microlenses are formed within the counter substrate of the liquid crystal display panel, and are structured so that the microlens are sandwiched between two glass plates.
With reference to FIG. 20(a) and (b), two typical methods for producing a counter substrate which is equipped with conventional microlenses will be described. Note that a plurality of microlenses which are in a regular arrangement will be collectively referred to as a microlens array.
The first production method produces a substrate (microlens array substrate) equipped with a microlens array, through steps (a-1) to (a-4) which are schematically shown in FIG. 20(a).
(a-1): A photoresist layer on a glass substrate is patterned.
(a-2): The patterned resist layer is heated to cause thermal flow, thus forming a resist layer having the shapes of microlenses.
(a-3): together with the resist layer having microlens shapes, the glass substrate is dry-etched in order to form the shapes of the resist layer on the glass substrate (etch back), whereby a microlens array substrate is obtained.
(a-4): Via an adhesion layer, cover glass is adhered to the resultant microlens array substrate, and the surface of the cover glass is polished, whereby a counter substrate is obtained. Note that, an electrode, an alignment film, and the like are formed as necessary.
The second production method produces a counter substrate equipped with a microlens array, through steps (b-1) to (b-4) which are schematically shown in FIG. 20(b).
(b-1): A photoresist layer on a glass substrate is patterned via electron beam exposure, for example, thus forming a resist layer having the shapes of microlenses. This is used as a master.
(b-2): Using the master, a metal stamper is produced, for example by plating technique.
(b-3): Using the metal stamper, the shapes of microlenses are transferred to the glass substrate, thus obtaining a microlens array substrate.
(b-4): Via an adhesion layer, cover glass is adhered to the resultant microlens array substrate, and the surface of the cover glass is polished, whereby a counter substrate is obtained.
Moreover, Patent Document 1 discloses a method in which, by utilizing the pixels of a liquid crystal display panel, a photosensitive material which is applied to the surface of a counter substrate is exposed to light, thus forming microlenses for the pixels through self assembly. This method has advantages in that misalignment between the microlenses and the pixels does not occur, and that the microlenses can be produced at low cost.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2002-62818